fix(jqLite): Check "length" in obj in isArrayLike for iOS JIT bug

[snapwich]

to prevent iOS8 JIT bug (https://bugs.webkit.org/show_bug.cgi?id=142792) from surfacing

This is the fix implemented in underscore.js and most likely the fix that will be implemented in jQuery.

It's not a very easy to recreate bug, but I stumbled upon it myself in our production app and was able to narrow it down to isArrayLike after several hours of banging my head. This plunkr was the closest I got to consistently surfacing the bug in Angular: http://plnkr.co/edit/UQ5NhZnRuafNxWiJuuyN

That ng-repeat will fail, but only on iOS8 (and i've personally only had it fail on iPad) about 50% of the time after a few digests. If it doesn't fail quick reloading the plunkr a few times will usually get it to fail.

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[snapwich]

Updated pull request to follow updated isArrayLike solution in jQuery jquery/jquery#2185

Unfortunately no tests since this is iOS8 only and doesn't surface in iOS simulator.

[realityking]

@snapwich Could you add a comment explaining why it's needed? Otherwise someone will probably try to remove it in a couple of months or years ;)

[snapwich]

@realityking sure. I just added a comment similar to the jQuery commit.

[snapwich]

Any update on merging this? This fix has made its way into jQuery now and would be a quick fix for Angular.

[caitp]

LGTM

[jdalton]

I believe jQuery found that based on their usage they didn't need the Object(...) use. Might be worth checking out here too.

[caitp]

@jdalton that works in jQuery's case because the caller knows that it's a non-null "object" already, I'm not sure the same assumptions fly here. It would be good to make those assumptions work but I won't consider that a blocker

[snapwich]

@jdalton @caitp yeah jQuery and Angular make some different assumptions I think.

Removing the Object(...) causes these unit tests to fail that otherwise don't:

angular forEach should handle string values like arrays FAILED
angular forEach ES spec api compliance should follow the ES spec when called with string FAILED

[petebacondarwin]

For reference jquery/jquery#2145

[petebacondarwin]

@mzgol - you worked on this bug in JQuery - what is your recommendation here?

[mgol]

We should work around it; relevant jQuery commit: jquery/jquery@1541664

[mgol]

This looks good but in jQuery it turned out some people relied on undocumented behavior that jQuery.map worked on strings and not just arrays (this broke a popular DataTables jQuery plugin, they've already fixed it so we didn't touch the final implementation). Not sure if this is an issue here.

[petebacondarwin]

OK, LGTM. Let's merge this.